1. Field of the Invention
One or more embodiments of the present invention relate to an anode active material, a lithium secondary battery including the anode active material, and a method of preparing the anode active material, and more particularly, to an anode active material that is improved in terms of cycle characteristics, initial efficiency, and discharge capacity, and a lithium secondary battery including the anode active material, and a method of preparing the anode active material.
2. Description of the Related Art
Lithium secondary batteries used in portable electronic devices for information communications, such as personal data assistants (PDAs), mobile phones, and laptop computers, electric bicycles, electric vehicles, and the like have a higher discharge voltage about twice or more as compared with existing batteries, and thus exhibit a high energy density.
Lithium batteries include a cathode and an anode, each including an active material that allows intercalation and deintercalation of lithium ions, and an organic electrolyte or a polymer electrolyte filling the gap between the anode and cathode. Lithium batteries produce electrical energy from redox reactions that take place as lithium ions are intercalated into or deintercalated from the cathode and anode.
Carbonaceous materials in various forms, such as artificial graphite, natural graphite and hard carbon, which allow intercalation and deintercalation of lithium ions, and non-carbonaceous materials such as high-capacity silicon (Si) have been studied for use as anode active materials of lithium secondary batteries.
However, non-carbonaceous materials such as Si may destabilize an anode structure as a result of repeated expansions and shrinkages during intercalation/intercalation of lithium ions, and thus may deteriorate cycle characteristics. To address these drawbacks, there has been research into Si-based alloy materials.
In general, Si-based alloy materials may consist of an active Si phase, and an inactive alloy phase serving as a matrix. The active Si phase includes Si crystal particles.
Si-based alloy materials have a structure in which a matrix structure, as a buffer layer for suppressing volumetric expansion of the Si crystal particles during charging/discharging of a lithium secondary battery, is surrounded by Si crystal particles. Furthermore, to improve cycle characteristics of the lithium secondary battery, there have been used methods of preparing a Si-based alloy material to have smaller Si crystal particles.
However, such preparation methods may likely cause residual stress in the Si-based alloy material during charging/discharging of the lithium secondary battery, and may not provide sufficient migration paths of Li ions coming from the cathode during charging of the lithium secondary battery or allow accommodation of Li ions.
Therefore, there still is a need for the development of an anode active material with improved cycle characteristics, initial efficiency and discharge capacity, a lithium battery including the anode active material, and a method of preparing the anode active material.